The invention relates to a current sensor which works with a toroidal body, through which at least one conductor to be evaluated is extended and from which a measuring signal is taken. Such current sensors are commonly designed ss current-transformers with an iron core or in the form of a Rogowski transformer without iron. Such transformers have complicated winding forms over a toroidal round body, the manufacture of which is costly and time-consuming.
It is an object of the present invention to develop a current sensor for measuring the currents and differential currents free of potential, and which can be manufactured simply and cost-effectively.
According to the invention, the object is achieved through the use of a toroidal body which comprises a magnetostrictive material and conductor runs applied to the toroidal body over at least one ring region. The conductor runs are made from length-dependent resistance material. The resistance change of the conductor runs is evaluated in a manner to determine a value, e.g., a current value, representative of the current in a conductorto be measured.
Such a current sensor has no need for the otherwise required costly pushed-through turns. The primary winding can be constructed in the usual manner from a single or multiple insertion turns. Although wire strain gauges have been known for a long time, they have not been utilized for the design of a simple but relatively accurate current sensor.
It is advantageous to extend the conductor runs of length-dependent resistance material over the entire circumference of the toroidal body in order to eliminate length changes along the toroidal body such as can occur with strong external fields. In order to also keep external field influences on the conductor runs low, it is advantageous to make the conductor runs as loops comprising forward and return conductors. This stimulates bifilar lines.
If a center tap of a loop is brought out as the third terminal in addition to the two end terminals of the loop, partial resistors are obtained which can be used in bridge circuits. Several loops of the conductor runs can also be connected in series.
The invention will now be explained in greater detail, referring to an exemplary embodiment shown schematically in the drawing.